Field of the Invention
The present invention relates to a power transmitting apparatus, a power receiving apparatus, a power transmitting method, a power receiving method, and a program.
Description of the Related Art
In 2010, the “Qi Standard” was established by the Wireless Power Consortium (WPC) for mobile apparatuses having a power of 5 watts or less. Since then, non-contact power supply apparatuses for smart phones and mobile phones have been spreading. Most of non-contact power supply apparatuses currently on the market are of the electromagnetic induction type having a power transmission distance of several millimeters to several centimeters.
In late years researches have been rapidly progressing on the magnetic field resonance method for achieving power transmission over a distance of several centimeters to several meters, as a non-contact power supply method other than the electromagnetic induction method. The magnetic field resonance method is a method for transmitting the power through magnetic field resonance of a resonator composed of a coil and a capacitor embedded on each of the power transmitting and the power receiving sides. The power receiving side converts a high frequency generated by resonance into a direct current (DC) signal by using a rectification circuit, and uses the DC signal as the power.
There are reported a technique for transmitting a 60-watt power over a 2-meter distance by using the magnetic resonance method, and a development of a wireless power supply system for driving an electronic apparatus at a 50-centimeter distance by using a 60-watt power. In connection with the magnetic field resonance method, there is expected a development of a product having a new concept of extending the power transmission distance up to about 10 meters in the future, and wirelessly supplying the power to office and home electric appliances.
One of technical problems in using the magnetic field resonance method is that, when power supply ranges of a plurality of power transmitting apparatuses overlap with each other, a certain power transmitting apparatus may supply the power to an unintended device. In this case, the following problems may possibly occur.
(1) The efficiency of power supply to a correct device decreases.
(2) Supplying a high power to an unintended device damages the device.
(3) When the power is charged, the power is intentionally or unintentionally stolen.
To solve the above-described problems, there is a proposed an apparatus having a communication unit and a circuit capable of dynamically changing the resonance frequency between a power transmitting apparatus and a power receiving apparatus (see, for example, Japanese Patent Application Laid-Open No. 2011-166883). The present apparatus changes a resonance frequency fn for power supply to a device, to frequencies f0, f1, f2, f0, at suitable intervals on a time sharing basis. This technique enables reducing the possibility of unintended power supply to ⅓ or below (generally to 1/n or below) even if another device having the resonance frequency f0 is placed in the vicinity of the apparatus.
However, in the technique discussed in Japanese Patent Application Laid-Open No. 2011-166883, the power transmitting apparatus needs to repetitively change the resonance frequency in power transmission to one power receiving apparatus. Therefore, there has been a problem that a mechanism for changing the resonance frequency becomes complicated resulting in complicated processing. Moreover, there has been a problem that unintended power supply may occur.